Fish oil in known to have significant antiproliferative and anticancer effects in humans and experimental animals. In previous studies, we have identified a novel effect of fish oil on S-phase progression. Both in vivo and in vitro studies have shown that S-phase duration is significantly longer following fish oil supplementation. These effects are associated with a change in the activity at the replication origin (ori-beta) located within the dihydrofolate reductase (DHFR) gene in CHO cells. We have also shown that fish oil alters the chromatin structure in cells where the effect of this oil on S-phase is expressed. Both S-phase prolongation and the change in chromatin structure are reversed by addition of the polyamine precursor putrescine to the culture media. Our hypothesis is that fish oil affects the duration of S-phase by altering the spatial and/or temporal organization of replication origins. We postulate that elucidation of the mechanism(s) by which fish oil alter(s) S-phase and cell cycle progression will depend on further understanding of the molecular mechanisms that organize replication origins at specific DNA sites in mammalian cells. In this small grant application, we propose to initiate studies that will facilitate future research on the role of nutrients in DNA replication. Initially, we will identify and characterize the activity of ori-beta, ori-beta', and ori-gamma, following fish oil and PUFA treatment by use of a detailed nascent DNA mapping technique. This study will test whether fish oil suppresses ori-b and activates secondary replication sites, or whether this treatment alters the location of replication origins. We will also conduct feasibility experiments to test the applicability of genomic DNA mapping and cross-linking/chromatin immunoprecipitation (CHIP) techniques in studies of replication protein/DNA interactions within the DHFR gene locus. The results of this small application will help us design a full research project to determine the molecular targets and mechanism of action of fish oil and PUFA on DNA replication.